The following abbreviations and terms are herewith defined:
AMC adaptive modulation and coding
BS base station (e.g., network access node)
DL downlink
DRA distributed resource allocation
FDM frequency division multiplex
FUSC full usage of subchannels
IEEE institute of electrical and electronics engineers, Inc.
IMT international mobile telecommunications
LRA localized resource allocation
OFDM orthogonal frequency division multiplex
OFDMA orthogonal frequency division multiple access
PHY physical-layer
PUSC partial usage of subchannels
RB resource block
STBC space-time block coding
SFBC space-frequency block coding
SM spatial multiplexing
TG task group
UE user equipment (e.g., mobile station MS or subscriber station SS)
WiMAX worldwide interoperability for microwave access
IEEE 802.16 working group has established a new task group (TG), 802.16 TGm, to amend 802.16 specifications. See for example IEEE 802.16Rev2/D3, “IEEE draft standard for Local and Metropolitan Area Networks—Part 16: Air interface for fixed Broadband Wireless Access systems”, February 2008, hereby incorporated by reference. The 802.16m amendment targets at providing an advanced air interface to meet the IMT-Advanced requirement, as seen at “IEEE 802.16m System Requirements” (document IEEE 802.16m-07/002r4), attached as Exhibit A to incorporated U.S. Provisional Patent Application No. 61/123,723.
During an IEEE 802.16m meeting held in Orlando, Fla. during March, 2008, a high-level subchannelization procedure has been proposed to support the concept of fractional frequency reuse. See for example “Symbol Structure Design for 802.16m—Resource Blocks and Pilots (document IEEE C802.16m-08/121r1) and “Design of Resource Allocation Unit Structure for IEEE 802.16” (document IEEE C802.16m-08/188r3), attached as respective Exhibits B and C to incorporated U.S. Provisional Patent Application No. 61/123,723. This subchannelization procedure is summarized generally as follows:                PHY resource blocks (RB) of the overall bandwidth are firstly permuted and partitioned to frequency reuse groups. Each group contains a specific set of RBs (e.g., the whole bandwidth is partitioned into 3 frequency reuse groups, with the reuse factors equal to 1, 2 and 3 respectively.)        Within each frequency reuse group, the localized resource allocation (LRA) and distributed resource allocation (DRA) are done in a FDM manner. That is, some PHY RBs are used for LRA, and the others are permuted and then used for DRA.        
This high-level concept is much more flexible than subchannelization under the IEEE 802.16e standard. In 802.16e, FUSC/PUSC/AMC zones could only be defined in a TDM manner, i.e., a number of sequential OFDMA symbols is either used for DRA (i.e. FUSC/PUSC) or used for LRA (i.e. AMC). The FDM manner is seen to have a natural advantage of finer granularity than the TDM manner, which is intended to result in higher efficiency in terms of resource utilization.
Besides the frequency domain diversity, the FUSC/PUSC subchannelization of the 802.16e standard has the favorable property of inter-cell/sector interference averaging, which is primarily gained by doing permutation. After permutation, the number of “subcarrier hits” between any subchannels in different cells or sectors is minimized, so that the interference between subchannels in different (adjacent) cells or sectors is minimized. A single “subcarrier hit” means that the two subchannels in two different cells/sectors contain one same physical subcarrier. In other words, it means an inter-cell/sector subcarrier collision.
There is a problem on how to flexibly do LRA and DRA within one frequency reuse group without losing the above benefit of the inter-cell/sector interference averaging. It is noted that in 802.16e, this problem does not exist because LRA and DRA are done in a TDM manner. Consider a straightforward subchannelization method. First, a number of PHY RBs are selected for LRA based on channel state information. The other PHY RBs are left for DRA. Second, permutation (similar to the FUSC/PUSC permutation done in 802.16e) is done within the DRA PHY RBs to get the subchannels for DRA. The subcarriers in these subchannels are spread over all the DRA PHY RBs.
The above generalized approach leads to several drawbacks:                To do the LRA and DRA flexibly, the ratio between the number of LRA RBs and the number of DRA RBs should be flexible, which means that the number of DRA RBs should be variable. This needs a very large number of specific permutation sequences of different lengths, because the length of a permutation sequence should be equal to the number of DRA subchannels (at least according to the permutation scheme in 802.16e). Naturally, the number of DRA subchannels is determined by the number of PHY RBs for DRA. This very large number of possible permutation sequences will complicate implementation of a system under IEEE 802.16m.        A more serious problem arises for interference concerns. Even if there are many permutation sequences of different lengths, the low number of subcarrier hits between different cells/sectors in 802.16 cannot be kept. In one frequency reuse group, the set of PHY RBs selected for LRA is different among different cells/sectors due to the different channel states in that sector. Thereafter, the set of PHY RBs selected for DRA are different among different (adjacent) cells/sectors, and so the benefit of permutation is foregone.        
Note that in 802.16e, the permutation is designed based on specific sequences, like a Reed-Solomon code. One beneficial property of such a sequence is that the sequence is still a Reed-Solomon code after being cyclically shifted or being modulo-added with some fixed number. Another positive property is that any different pair of Reed-Solomon codes has the maximum possible Hamming distance between them. Therefore, when the PHY resources selected for DRA are the same among different cells/sectors, by using the permutation, subchannels from different cells/sectors will have a very small number of subcarrier hits. U.S. Pat. No. 7,224,741 provides a more detailed explanation for the Reed-Solomon code advantage in this regard. But as noted above, when the PHY RBs selected for DRA are different among different cells/sectors, the interference reducing properties of the permutation cannot be sustained.